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 A065585 Smallest prime beginning with exactly n 2's. 6
 3, 2, 223, 2221, 22229, 2222203, 22222253, 22222223, 222222227, 22222222273, 22222222223, 2222222222243, 22222222222201, 22222222222229, 222222222222227, 222222222222222043, 222222222222222281, 222222222222222221, 22222222222222222253, 222222222222222222277 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 LINKS M. F. Hasler, Table of n, a(n) for n = 0..200 MATHEMATICA Do[a = Table[2, {n}]; k = 0; While[b = FromDigits[ Join[a, IntegerDigits[k] ]]; First[ IntegerDigits[k]] == 2 || !PrimeQ[b], k++ ]; Print[b], {n, 1, 17} ] PROG (PARI) A065585(n)={n=10^n\9*2; n>2&for(d=1, 9e9, n*=10; for(t=1, 10^d-1, t\10^(d-1)==2 & t+= 10^(d-1)+(t>2); ispseudoprime(n+t) & return(n+t))); 2+!n} \\ M. F. Hasler, Oct 17 2012 (Python) from sympy import isprime def a(n): if n < 2: return list([3, 2])[n] n2s, i, pow10, end_digits = int('2'*n), 1, 1, 0 while True: i = 1 while i < pow10: istr = str(i) if istr[0] == '2' and len(istr) == end_digits: i += pow10 // 10 else: t = n2s * pow10 + i if isprime(t): return t i += 2 pow10 *= 10; end_digits += 1 print([a(n) for n in range(20)]) # Michael S. Branicky, Mar 02 2021 CROSSREFS Cf. A037057, A065584 - A065592. A068103 is a lower bound, but most often equality holds. - M. F. Hasler, Oct 17 2012 Sequence in context: A297532 A369990 A037057 * A139737 A354386 A036113 Adjacent sequences: A065582 A065583 A065584 * A065586 A065587 A065588 KEYWORD nonn,base AUTHOR Robert G. Wilson v, Nov 28 2001 EXTENSIONS Corrected by Don Reble, Jan 17 2007 STATUS approved

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Last modified May 22 17:27 EDT 2024. Contains 372758 sequences. (Running on oeis4.)